1. Field of the Invention
This invention relates to wireless communication systems, and more particularly to a wireless communication system that provides telephone, data and Internet connectivity to a plurality of users.
2. Description of Related Art
Several systems are currently in place for connecting computer users to one another and to the Internet. For example, many companies such as Cisco Systems, provide data routers that route data from personal computers and computer networks to the Internet along conventional twisted pair wires and fiber optic lines. These same systems are also used to connect separate offices together in a wide area data network.
However, these systems suffer significant disadvantages because of the time and expense required to lay high capacity communications cables between each office. This process is time consuming and expensive. What is needed in the art is a high capacity system that provides data links between offices, but does not require expensive communication cables to be installed.
Many types of current wireless communication systems facilitate two-way communication between a plurality of subscriber radio stations or subscriber units (either fixed or portable) and a fixed network infrastructure. Exemplary systems include mobile cellular telephone systems, personal communication systems (PCS), and cordless telephones. The objective of these wireless communication systems is to provide communication channels on demand between the subscriber units and the base station in order to connect the subscriber unit user with the fixed network infrastructure (usually a wired-line system). Several types of systems currently exist for wirelessly transferring data between two sites.
In wireless systems using multiple access schemes, frames of time are the basic transmission unit. Each frame is divided into a plurality of slots of time. Some time slots are used for control purposes and some time slots are used for information transfer. Information is typically transmitted during time slots in the frame where the time slots are assigned to a specific subscriber unit. Subscriber units typically communicate with the base station using a xe2x80x9cduplexingxe2x80x9d scheme which allows for the exchange of information in both directions of connection.
Transmissions from the base station to the subscriber unit are commonly referred to as xe2x80x9cdownlinkxe2x80x9d transmissions. Transmissions from the subscriber unit to the base station are commonly referred to as xe2x80x9cuplinkxe2x80x9d transmissions. Depending upon the design criteria of a given system, the prior art wireless communication systems have typically used either time division duplexing (TDD) or frequency division duplexing (FDD) methods to facilitate the exchange of information between the base station and the subscriber units. Both the TDD and FDD duplexing schemes are well known in the art.
In TDD systems, duplexing of transmissions between a base station and its subscriber units is performed in the time domain. A selected subscriber unit typically communicates with a selected base station using a specific pre-defined radio frequency. The channel is time-divided into repetitive time periods or time xe2x80x9cslotsxe2x80x9d which are employed for uplink and downlink transmissions. In contrast to FDD systems, frequency allocation or frequency reuse patterns are simplified because there is no requirement of frequency separation between the uplink and downlink transmissions.
Both the uplink and downlink transmissions occur during different pre-determined time slots using the identical radio frequency. In some current wireless communication systems, there are base stations that act as central points for receiving and transmitting data to a plurality of customer sites. These base stations typically connect to other data systems such as the Internet, the phone system or other systems that provide user data to the customer""s sites. As can be imagined, it is important to maintain a strong signal between the base station and the customer sites. Thus, in conventional systems, power detectors within the base station and customer sites continually monitor wireless transmissions in order to tune the system to receive the strongest possible signal.
Unfortunately, prior customer sites relied on complicated control signals to measure transmission power levels. These control signals were implemented because in TDD systems the transmit and receive paths use the same frequency. Thus, it was possible that when the customer site equipment took a power measurement, it was actually measuring a transmission signal from a nearby customer site that was transmitting on the same frequency. The addition of the control signals ensured that power measurements were taken from the base station, and not a nearby customer site.
Moreover, in some prior systems, the customer site equipment was separated into indoor units and outdoor units. The indoor units typically included the modem and electronics for connected with the customer""s equipment. The outdoor unit was installed on the exterior of the building and included the antenna for receiving and transmitting wireless user data. However, in these systems, the outdoor unit did not independently know when the base station was transmitting.
Some prior systems attempted to solve this problem by including a gating signal between the indoor unit and the outdoor unit. The gating signal could be used to instruct the outdoor unit to sample its receive detectors at a particular time, thus ensuring that the receive detectors would measure signals from the base station. Unfortunately, adding this signal to the transmission cable between the outdoor unit and the indoor unit requires costly hardware changes. In addition, transmitting the extra gating signal across the transmission cable increases spurs and other undesirable effects in the data transmission pathway.
This problem is compounded by the fact that the outdoor unit does not contain a modem. A modem could serve as a conduit for the outdoor unit to receive additional commands. Thus, the outdoor unit, by itself, cannot determine the proper time to sample the receive detectors.
Thus, what is needed in the art is a convenient system at the customer site for accurately measuring the power of transmission signals from the base station. Such a system is described below.
One embodiment of the invention is a wireless communication system having a plurality of base stations and customer sites, wherein data is transferred between said base stations and said customer sites, and wherein said system comprises preset downlink time segments for transmitting said data between the base stations and the customer sites. This embodiment includes: an indoor unit comprising a first modem configured to modulate/demodulate data transmitted between the base stations and the customer sites, wherein the indoor unit is adapted to transmit a control message at a predetermined time with respect to said preset downlink time segments; an outdoor unit comprising a micro controller and a signal detector, said outdoor unit being adapted to receive the control message and, in response to receiving said control message, read said signal detector; and a broadband cable linking the indoor unit to the outdoor unit.
Another embodiment of the invention is a wireless communication system having a plurality of base stations and customer sites, wherein data is transferred between said base stations and said customer sites, and wherein said system comprises preset downlink time segments for transmitting said data between the base stations and the customer sites. This embodiment includes: an indoor unit comprising a first modem configured to modulate/demodulate data transmitted between the base stations and the customer sites, said indoor unit further comprising a programmable memory adapted to transmit a control message at a predetermined time with respect to said preset downlink time segments; an outdoor unit comprising a micro controller and a signal detector, said outdoor unit being adapted to receive the control message and, in response to receiving said control message, read said signal detector; and a broadband cable linking the indoor unit to the outdoor unit.
Yet another embodiment of the invention is a method for measuring the strength of a signal transmitted from a base station to a customer site in a wireless communication system, wherein said wireless communication system has preset downlink time segments for transmitting data from the base station to the customer site, and wherein said customer site comprises an indoor unit and an outdoor unit. This method provides: transmitting a message from said indoor unit to said outdoor unit, wherein said message is timed to arrive at said outdoor unit at a predetermined time relative to said preset downlink time segment; and reading a detector in said outdoor unit in response to receipt of said message so that said detector is read during said preset downlink time segment.
Still another embodiment of the invention is a method for tuning a wireless communication system, wherein said wireless communication system has preset downlink time segments for transmitting data from a base station to a customer site, and wherein said customer site comprises an indoor unit having a processor and an outdoor unit having tunable attenuators. This method includes: transmitting a control message from said indoor unit to said outdoor unit, wherein said message is timed to arrive at said outdoor unit at a predetermined time relative to said preset downlink time segment; reading a detector in said outdoor unit in response to receipt of said message so that said detector will be read during said predetermined downlink time segment; transmitting a response message comprising values from said detector to said indoor unit; determining the appropriate settings said attenuators in said outdoor unit; transmitting a second control message comprising updated attenuator settings to said outdoor unit; and tuning said outdoor unit based on said updated attenuator settings.